Prevention of gauge bands in rolls of film

ABSTRACT

A core used in winding plastic film provided with a compressible liner at areas of the core which tend to develop gauge bands when plastic film is wound in a roll about the core. The liner rests in an undercut portion of the core. The core is capable of preventing gauge band formation in plastic film wound thereabout.

UNITED STATES PATENTS C Unlted States Patent [191 [111 3,737,030

Stewart [4 1 June 5, 1973 54 PREVENTION OF GAUGE BANDS IN 3,179,2454/1965 Bastian, .Ir. ...242/68.5 x ROLLS 0F FILM 3,433,355 3/1969 Smith..242/68.5 x

v [75] I Inventor: Donald F. Stewart, Whippany, Primary Examiner- GeorgeE Lowrance [73] Assignee: Allied Chemical Corporation, New AssistantExaminersteven E.Lipman York, NY, Att0rney-Jonathan Plaut and Roger H.Criss [22] Filed: Oct. 27, 1971 [57] ABSTRACT [2]] Appl' 192986 A coreused in winding plastic film provided with a compressible liner at areasof the core which tend to [52] US. Cl. ..206/59 E, 242/685 develop gaugebands when plastic film is wound in a [51] Int. Cl ..B65d 85/67, B65 h75/02 roll about the core. The liner rests in an undercut por- [58]Field of Search ..206/58, 59 R, 59 E; tion of the core. The core iscapable of preventing 242/685, 68.6 gauge band formation in plastic filmwound thereabout. [56] ReferencesCited 11 Claims, 6 Drawing FiguresPatented June 5, 1973 FIG?) R O R P ART PREVENTION OF GAUGE BANDS INROLLS OF FILM BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to the formation and winding of plastic films,particularly extruded plastic films which are wound on rolls.

2. Description of the Prior Art In the process of forming plastic films,it is often difficult to precisely control the uniformity of filmthickness (gauge). As a result, products such as extruded plastic filmsat times possess areas of increased thickness due to variations in thecross-sectional size of the extruding die or other factors. For example,in extrud-. ing a flat plastic film one point or portion of theextruding die slot may be of a slightly greater cross-section than thatdesired which results in an area of slightly increased cross-section inthe film extending along the longitudinal axis of the film. When suchfilms are wound about a core or mandrel for storage or shipment, theeffect of the superimposition of even minor variations in thickness ineach convolution is reflected, especially in the outer windings, asheavy or thick circumferential bands, commonly referred to as gaugebands. Such gauge bands, which generally are ridges exhibiting a colordarker than the remainder of the plastic film, tend to cause the film,primarily the outer wraps thereof, to distort and stretch at the thickersections during winding and following removal of the winding tension. Itis found that upon unwinding such distortion is permanent whereby theutility of the film for converting into bags or for printing or otherpurposes is impaired.

As another example, plastic film used as shrinkage film is generallystretched during processing to impart the desired molecular orientationcharacteristics to the film. As a result of this stretching, marginalsections of the film tend to be of a thicker gauge than the centerportions of the film. These marginal sections may cause gaugebands toform in the marginal portions of a roll of the film.

One present procedure for eliminating gauge bands in the final productis to rewind the film on the roll and slit to remove the distorted areasof the film. This procedure is costly due to the necessity for rewindingthe film and wastage due to cutting. Attempts have been made in thepast, with varying degrees of success, to prevent gauge bands fromforming in rolls of plastic film. For example, extruding molds have beenprovided with rotating or shifting means in order to circumferentiallyrotate or laterally oscillate the blown or flat film during extruding.This results in a circumferential or lateral shifting of the thickerareas of the plastic film such that when the film is wound as a roll ona core, the thicker areas of each convolution or series of convolutionsare displaced along the longitudinal axis (i.e., width) of the rollrather than directly overlying and building upon the thicker areas ofprevious windings. In this manner, gauge band formation is prevented.Both flat and circular molds and/or their respective forming and/orcollecting rolls have been provided with lateral shifting means. Theaddition of such means to existing mold lines, however, involvessubstantial expenditures.

It has been proposed in U.S. Pat. No. 3,249,216, issued May 3, I966 toPhillips et al., to eliminate hard circumferential bands in rolls ofplastic film by including a particulate material between adjacentconvolutions. This procedure, however, requires an additional stepduring the winding process and a very careful application of extraneousmaterial to the film. When particulate material is applied to a filmhaving a clinging or tacky surface, such as plastic film used for 'meatpackaging, it was found that the film often lostits desired tackiness.In addition, in certain instances other desired surface properties ofsuch film were impaired, such as sealability. It has been proposed inU.S. Pat. No. 3,390,762, issued July 2-, 1968 to Mernieks to preventirregularities due to distortion of the leading edge of plastic film asit is wound about the core from reflecting in and resulting in damage tosubsequent layers by including a foamed insert in part in contiguousrelation with the core and in part over the leading edge of the film orbetween the first circumvolutions of the film. The solution to thisproblem also requires an additional step during the winding operationand a very careful application of an extraneous material during winding.

OBJECTS OF THE INVENTION An object of this invention is to provide arelatively low cost, effective means of preventing gauge bands fromforming in plastic films.

Another object of this invention is to provide a gauge band-preventingmeans which can be incorporated into existing commercial plastic filmproduction lineswithout substantial capital expenditure and withoutadding an additional step requiring careful control to the windingoperation.

Other objects and advantages of the invention may be apparent from thedescription which follows or from the drawings.

SUMMARY OF THE INVENTION Formation of gauge bands in rolls of plasticfilm is substantially prevented by providing the supporting winding coreor mandrel with undercut portions extending circumferentially around thecore periphery which are filled with a liner formed of a compressiblematerial. These filled undercut portions are provided at the locationson the core at which the gauge bands would otherwise form when the filmis wrapped around the core. It is believed that when plastic film iswrapped about such selectively linedcores, the film is free to expand inthe radially inward direction due to the nature of the liner material aswell as expand in the radially outward direction due to the fact thatthe outer layer of the roll is under no restraint. As a result, there islittle or no gauge band build-up because thickness irregularities inindividual convolutions of the film are allowed to even out in both theradial inward and outward directions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of awinding core of this invention.

FIG. 2 is an enlarged view of a section along line 2-2 of FIG. 1 showingthe relative position of the core liner and the core wall.

FIG. 3 is a cross-section view taken along line 3-3 of FIG. 1.

FIG. 4 is a side view of a roll of plastic film wound about a core ofthis invention.

FIG. 5 is a side view of a roll of plastic film wound about a core whichdoes not have an undercut portion.

FIG. 6 is a side view of a roll of plastic film wound about a core whichis provided with an undercut portion but without a liner insertedtherein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawings,particularly FIGS.

1-3, a winding core 10 having core walls 12 is provided with an undercutarea which is filled with a compressible liner material 14. Core 10 maybe a paper tube which is conventionally used for winding plastic filmbut cores formed from other materials such as aluminum, fibercomposition board, etc., may also be employed. The conventional papertubes are generally of substantially cylindrical shape and have a wallthickness of about one-half inch and a diameter of about 3 to 6 inches,although of course these dimensions are not critical. Although a hollowcore is shown in the drawings, the core could alternatively benon-hollow. An undercut or recessed portion 20 is provided in thoseareas of the core at which the plastic film to be wound thereabout tendsto develop gauge bands. The manner of locating these areas is describedbelow. Undercut area 20 may be of anysuitable depth, for example aboutone-eighth to one-fourth inch in a paper core having a- ,4 inch wallthickness, such that a portion 22 of core wall 12 preferably liesbeneath undercut portion 20. The thickness of undercut area 20 isgenerally dictated by the width of the corresponding gauge bands. Theundercut portion which extends circumferentially around the periphery ofthe core, may suitably be and preferably is a groove formed in the coreby a lathe or by other conventional techniques. Undercut portion 20 isfilled with an annular piece of any compressible liner material 14capable of yielding to the plastic film to be wrapped on the core. Theliner material, preferably of a soft nature, may be an adhesive tapehaving a foam backing, corrugated or crimped paper wadding, rubber, foamrubber, foamed plastics and other materials exhibiting the desiredproperties. Also, compressible composite materials, such as laminatedplastic film (e.g., polyethylene) having air pockets between the layerscould be used. Preferably, liner 14 is a foam-backed adhesive tape, suchas a polyurethane foam-backed adhesive tape, which is successively woundabout undercut portion 20 to fill the undercut portion to a desiredextent. As it is desired to provide a uniform radial thickness extendingacross the width of the core in order to encourage uniform gaugethickness of the film windings, the upper surface 16 of liner 14 shouldbe substantially coplanar and level with the outer surface 18 of corewall 12 adjacent undercut area 20. That is, liner 14 should be appliedto a depth such that the original core dimensions are maintained. Liner14 may also be in the form of a ring or strip of com-' pressible stockliner material which is inserted in undercut portion 20 and suitablyfixed in place.

Plastic film 24 is convolutely wrapped about core or mandrel 10 by aconventional technique, such as by providing a moving sheet of plasticfilm and revolving the core, which is suitably mounted, to wind the filmthereabout. At least a portion of the liner supports and is compressedby the plastic film wound about the core. This invention may be used inconjunction with plastic film made by any method, although it isparticularly useful with extruded plastic film produced from a flat orcircular die because gauge bands tend to be more exaggerated in extrudedfilms. The plastic film itself may be of any film-forming composition,such as nylon, polyvinyl chloride, polyolefins such as polyethylene andpolypropylene, polyesters, polyvinyl acetate, vinylidene chloridecopolymers, cellulose, polyurethane and other plastic films, as well asrubber sheeting.

As mentioned above, liners 14 are provided at those areas on core 10corresponding to areas of wrapped film 14 which tend to develop or formgauge bands. ln some cases, the location of these areas can beadequately predetermined prior to winding. For instance, as describedabove plastic shrink film tends to laterally distort during thestretching with a consequent buildup of film thickness along marginalportions. To eliminate the tendency of these thicker portions to buildupon each other and form gauge bands which distort the film especiallyin the outer windings, a marginal end or ends of the core are providedwith undercut areas which are thereafter filled with a suitable linermaterial. Another situation in which the location of gauge bandformation may be reasonably predetermined is in the winding of foldedplastic film. The area surrounding the fold line tends to present anincreased thickness when being wound. Therefore, the area of the corewhich supports the fold area of the wound film should be provided withthe recessed liner of this invention. 1

In instances wherein the location of the gauge band areas cannot bepredetermined to a satisfactory extent, the film may be wound on thecore for a few revolutions to determine the location of the gauge bands.The core may then be unwound, undercut areas provided where required anda liner placed in the undercut areas. Alternatively, undercuts could beprovided in a' second core at the required areas and the film woundabout this second core, with the first core being discarded. In thismanner, by making a sample run with only a small amount of filmmaterial, the gauge band formation areas can be adequately located andprovided with the undercut and liner of this invention such that acomplete roll of film can then be wound which is substantially free ofgauge bands.

FIG. 4 shows a roll of plastic film 24 wound about the improved core 10of this invention in which a liner 14 is placed adjacent marginal endportion 28 of core 10. The core is generally wider than the roll offilm. The plastic film has a marginal end portion 26 which has aslightly greater gauge and hence would otherwise tend to develop gaugebands at the marginal end portions of the roll. As shown in exaggeratedview, liner 14 is compressed to a degree by the weight of wound film 24.Distortion forces during and following windings are allowed to encourageinward gauge growth as well as outward expansion of the film. Inwardgauge growth is possible due to the compressible nature of the linermaterial. As a result, gauge bands are prevented from forming or theyare present to a much less pronounced degree.

FIG. 5 illustrates a roll of plastic film 24 wound about a conventionalcore 50 which is not provided with an undercut portion. This figureillustrates in an exaggerated view gauge band 30 which has formed due tothe superimposition of slightly thicker marginal end portions 26 whenfilm 24 is wound in a roll about core 50.

If a core'or mandrel were provided with undercut portions withoutfilling or lining such portions as herein disclosed, a roll of plasticmaterial wound about such core would tend to distort into the undercutareas with resultant damage to the film. This is shown in FIG. 6 whereinit is apparent that inward convolutions of film 24 are distorted intothe undercut groove 32 formed in core 60.

It is to be understood that variations and modifications of the presentinvention may be made without departing from the scope of the invention.It is also to be understood that the scope of the invention is not to beinterpreted as limited to the specific embodiment disclosed herein, butonly in accordance with the appended claims when read in light of theforegoing disclosure.

I claim:

1. A winding core adapted to be wound with a roll of film havingvariations in thickness across its width, said and said liner arelocated adjacent a marginal end of said core and are adapted to supporta marginal portion of said roll of film.

5. The core of claim 2 wherein said core has undercut portions adjacentboth marginal edges thereof and wherein resilient liners fill saidundercut portions.

6. The core of claim 2 wherein the outer surface of said liner issubstantially coplanar with the outer surface of said core adjacent saidundercut area.

7. The core of claim 2 wherein said core is substantially cylindrical inshape and is formed of paper.

8. The core of claim 2 wherein said liner is formed from materialselected from the group consisting of foam-backed adhesive tape,corrugated or crimped paper wadding, rubber, foam rubber, foamedplastics and laminated plastic film having air pockets between thelayers thereof.

9. A roll of plastic film wound in successive convolutions about a core,said core being provided with an undercut portion extendingcircumferentially around the periphery of said core and a resilientliner filling said undercut portion, at least a portion of said linersupporting and being compressed by said roll of plastic film.

10. A roll as claimed in claim 9 wherein said plastic film comprisespolyvinyl chloride shrink film.

11. A roll as claimed in claim 10 wherein said core is substantiallycylindrical in shape and is formed of paper.

1. A winding core adapted to be wound with a roll of film havingvariations in thickness across its width, said core being provided withan undercut portion extending circumferentially around the periphery ofsaid core and a compressible liner filling said undercut portion, saidundercut portion being located in an area of said core at which gaugebands would otherwise develop when said film is wound about said core.2. The core of claim 1 wherein said film comprises plastic film.
 3. Thecore of claim 2 wherein said undercut portion comprises a groove.
 4. Thecore of claim 2 wherein said undercut portion and said liner are locatedadjacent a marginal end of said core and are adapted to support amarginal portion of said roll of film.
 5. The core of claim 2 whereinsaid core has undercut portions adjacent both marginal edges thereof andwherein resilient liners fill said uNdercut portions.
 6. The core ofclaim 2 wherein the outer surface of said liner is substantiallycoplanar with the outer surface of said core adjacent said undercutarea.
 7. The core of claim 2 wherein said core is substantiallycylindrical in shape and is formed of paper.
 8. The core of claim 2wherein said liner is formed from material selected from the groupconsisting of foam-backed adhesive tape, corrugated or crimped paperwadding, rubber, foam rubber, foamed plastics and laminated plastic filmhaving air pockets between the layers thereof.
 9. A roll of plastic filmwound in successive convolutions about a core, said core being providedwith an undercut portion extending circumferentially around theperiphery of said core and a resilient liner filling said undercutportion, at least a portion of said liner supporting and beingcompressed by said roll of plastic film.
 10. A roll as claimed in claim9 wherein said plastic film comprises polyvinyl chloride shrink film.11. A roll as claimed in claim 10 wherein said core is substantiallycylindrical in shape and is formed of paper.